Ceramic containing composite materials have been known for many years and have been the subject of extensive research due to their unique combinations of chemical, electrical, mechanical and thermal properties. For example metal matrix ceramic containing coatings have been widely used in gas turbine engines. Other ceramic based coatings are used in the semi-conductor industry. These coatings are often applied by depositing the ceramic containing composites onto the substrate using methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), thermal or kinetic spray techniques. See generally U.S. Pat. No. 4,288,495 and U.S. Published patent application No. 2003/0180565. These prior art methods for depositing a ceramic containing composite coating often require a large amount of time to deposit a small amount of material or are very expensive and require complex processing conditions.
Ceramic containing composites have also been used to make structures such as piston rings or honeycomb structures for use in exhaust gas purification apparatus. These ceramic containing composites are often made by forming a “green body” and subjecting the green body to hot air drying and firing. See generally U.S. Published patent application No. US 2003/0159619.
In addition, to CVD, silicon carbide structures are produced primarily by sintering or reaction bonded processes.
Sintered silicon carbide components are traditionally manufactured using a mixture of silicon carbide particles, a sintering aid such as boron or aluminum, and binders. The binders enable the powder to be poured and pressed into a mold to form a green body with adequate strength to allow handling. A low temperature heating cycle is used for slow burn out of the binder, and to protect against cracking of the green body. The piece is then put into a high temperature furnace where sintering occurs. Presence of the sintering aid causes the silicon carbide body to shrink (about 20%) at a temperature of approximately 2100° C., without use of external pressure. The final sintered structure is relatively free of porosity.
Reaction bonded silicon carbide components consist of silicon carbide particles and free silicon. Traditional manufacturing technology uses a powder mixture of silicon carbide particles, binders and possibly graphite particles which are pressed at high pressure into a shape to form a green body of relatively high density. The body is placed in a low temperature furnace for a drying and binder burn out. The body is then placed into a graphite container with granular silicon. The container is covered and placed into a furnace, which is heated to about 1600° C. Under these conditions, the silicon vaporises and wicks into the body to form a reaction bonded silicon carbide structure relatively free of porosity. Unlike sintered SiC, reaction bonded silicon carbide components do not shrink during manufacturing.
As with the ceramic containing coatings discussed earlier, ceramic containing structures are expensive and difficult to manufacture because of the large amount of time, energy and high capital investment necessary to convert the starting materials into a final product.
It is an object of the present invention to provide a thermal spray feedstock that can be used to prepare ceramic containing composite materials, i.e. coatings or free-standing structures.
It is a further object of the present invention to provide a method for preparing a feedstock for conventional thermal spray apparatus which can be used to produce a ceramic containing composite material, i.e. coating or free-standing structure, in a quick, efficient and simple manner.
It is still a further object of the present invention to provide a method for quickly and efficiently preparing ceramic containing composite materials, i.e. coatings or free-standing structures, using conventional thermal spray apparatus.